Patent GB-449669-A (GB)
Title: Machines for tapping screw-threads
IPC: B23G1/16
Filed: 1936-01-18
Abstract: 449,669. Tapping. HERBERT, Ltd., A., LLOYD, A. H., and JINMAN, C. H., Canal Road, Edgwick, Coventry. Jan. 18, 1936, No. 1677. [Class 83 (iii)] In a tapping-machine wherein the spindle is rotated by an electric motor controlled bv forward and reverse contactors which are interlocked to prevent both being energized at the same time, switching means are provided which are automatically operative, on completion of a tapping operation, to energize the reverse contactor. In a machine wherein the spindle is fed to the work by hand and returned by a spring a rod 16 slidable parallel to the spindle carries a block 19 which maintains the rod in the neutral position shown in Fig. 3 by means of levers 20 and a spring 21. The ends of a notch on the block engage levers 23, 24 which operate switches 26, 27, respectively for energizing the forward and reverse contactors 31, 32, Fig. 4. Both switches may be maintained open by a cam 29 on a hand lever. To start the machine the hand lever is moved from the stop position to the start position, thereby moving the cam 29 into the position shown in Fig. 3. The surfaces 36 of the cam allow the forward switch 26 to close before the reverse switch 27, thereby energizing the forward contactor 31 through a switch 34 coupled to the reverse contactor. As the contactor 31 closes, a switch 33 coupled thereto is opened to prevent energization of the reverse contactor 32. On completion of the tapping operation a collar on the spindle engages a lever to move the rod 16 axially upwards and open the switch 26, de-energizing the contactor 31 and allowing the switch 33 to close, whereupon the contactor 32 is closed and the motor reversed, When the spindle reaches the upper limit of its travel another collar thereon moves the rod 16 downwards to open the switch 27 and de-energize the contactor 32, thereby closing the switch 34 to rotate the spindle in the forward direction again. The rod 16 may be moved by hand to reverse the driving motor at any time, or to cause a quick stoppage by giving a temporary reversal thereto. In a machine having an automatic power feed, the spindle is driven from the motor through pick-off gears which also drive, through a reduction gear, a yielding clutch and further pick-off gears, a rack on the spindle housing. The spindle has axial play in the housing and is fed through a helical spring so that the feed may be slightly in excess of the tapping feed. A pair of cams 41, 42, Fig. 5, are driven by the feed mechanism and actuate the switches 26 27 similar to the switches 26, 27 in Figs. 3 and 4. The operation of the machine is similar to that of the hand fed machine except that a hand controlled switch 30a, Fig. 5, is provided in parallel with a switch connected to the forward contactor 31, the switch 30a being closed momentarily by the operator to energize the forward contactor and this circuit being maintained by the second switch until reversal takes place. When the spindle returns to its upper position the second switch remains open and brings the motor to rest. The invention enables an operator to control a number of machines or a single machine with a number of independent spindles.